1. Field of the Invention
The present invention relates to an inverter circuit suitably applicable to, for example, a display using organic EL (Electro Luminescence) elements. Moreover, the invention relates to a display including the above-described inverter circuit.
2. Description of the Related Art
In recent years, in the field of displays displaying an image, displays using, as light-emitting elements of pixels, current drive type optical elements of which light emission luminance changes depending on the value of a current flowing therethrough, for example, organic EL elements have been developed for commercialization. Unlike liquid crystal elements or the like, the organic EL elements are self-luminous elements. Therefore, in displays (organic EL displays) using the organic EL elements, color gradation is obtained by controlling the value of a current flowing through the organic EL elements.
As in the case of liquid crystal displays, the organic EL displays are of a simple (passive) matrix system and an active matrix system as a drive system. In the former system, a configuration thereof is simple; however, there is an issue such as difficulty in achieving a large and high-definition display. Therefore, at present, the active matrix system has been increasingly developed. In this system, a current flowing through a light-emitting element arranged in each pixel is controlled by a driving transistor.
In the above-described driving transistor, in some cases, a threshold voltage Vth or mobility μ temporally changes, or the threshold voltage Vth or mobility μ varies from one pixel to another due to variations in a manufacturing process. In the case where the threshold voltage Vth or mobility μ varies from one pixel to another, the value of a current flowing through the driving transistor varies from one pixel to another, so even if the same voltage is applied to gates of the driving transistors, light emission luminance varies from one organic EL element to another, thereby impairing uniformity of a screen. Therefore, as described in Japanese Unexamined Patent Application Publication No. 2008-083272, a display having a function of correcting a change in the threshold voltage Vth or mobility μ has been developed.
Correction of the threshold voltage Vth or mobility μ is performed by a pixel circuit arranged in each pixel. For example, as illustrated in FIG. 19, the pixel circuit includes a driving transistor Tr100 controlling a current flowing through an organic EL element 111, a writing transistor Tr200 writing a voltage of a signal line DTL to the driving transistor Tr100, and a retention capacitor Cs. In other words, the pixel circuit has a 2Tr1C circuit configuration. The driving transistor Tr100 and the writing transistor Tr200 each are configured of, for example, an n-channel MOS type thin film transistor (TFT).
FIG. 18 illustrates an example of voltage waveforms applied to the pixel circuit and an example of changes in a gate voltage Vg and a source voltage Vs of the driving transistor Tr100. A part (A) in FIG. 18 illustrates a state where a signal voltage Vsig and an offset voltage Vofs are applied to the signal line DTL. A part (B) in FIG. 18 illustrates a state where a voltage Vdd turning the writing transistor Tr200 on and a voltage Vss turning the writing transistor Tr200 off are applied to a writing line WSL. A part (C) in FIG. 18 illustrates a state where a high voltage VccH and a low voltage VccL are applied to a power supply line PSL. Moreover, parts (D) and (E) in FIG. 18 illustrate states where the gate voltage Vg and the source voltage Vs of the driving transistor Tr100 are momentarily changed depending on the application of voltages to the power supply line PSL, the signal line DTL and the writing line WSL.
It is obvious from FIG. 18 that a WS pulse P is applied to the writing line WSL twice in a period of 1 H, and threshold correction is performed by a first WS pulse P and mobility correction and signal writing are performed by a second WS pulse P. In other words, in FIG. 18, WS pulses P are used for not only signal writing but also threshold correction and mobility correction of the driving transistor Tr100.